The invention is based on an electropneumatic brake system of a rail vehicle, containing a direct action electropneumatic brake device and an indirect action compressed-air brake device.
Such an electropneumatic brake system is known, for example, from DE 38 036 39 A1. In this brake system, a signal which corresponds to the axle load is used in the electronic controller to modify a transmission between the brake cylinder request and the brake pressure in the brake cylinder with a load correction. This load signal is applied to a pressure regulator which generates a pilot control pressure of the direct brake as a function of the electric brake pressure request signal of the direct, electronically controlled brake. In contrast, the indirect pneumatic brake includes a control valve which generates a pilot control pressure of the indirect brake as a function of a main air line pressure. The pilot control pressures of the indirect pneumatic brake and of the electronically controlled, direct brake are subjected to boosting by a relay valve or even two relay valves and are combined by a shuttle valve which passes on the larger of the pilot control pressures to a pressure limiting valve in a more or less reliable fashion.
For the indirect pneumatic brake and an emergency brake device, the load signal is used to adjust the pressure limiting valve which limits the brake pressure in the brake cylinder, but only when full braking occurs. Such brake systems have the disadvantage that load correction is not carried out continuously on the service brake and the regulating range is shortened. This fact is represented in the diagram in FIG. 1, which shows the profile of the brake pressure C generated by the direct brake device, plotted against the braking request for three load states: empty, partially laden and fully laden. Accordingly, the full range of the braking request can be regulated completely from 0% to 100% only when the vehicle is fully laden. When the vehicle is empty, the brake pressure C is regulated only up to approximately 30% of the braking request and is limited to a maximum value for a braking request which exceeds this. In an analogous fashion, the regulating range is also restricted when the vehicle is partially laden, which entails disadvantages in terms of the braking distance.